A variety of workpieces may have or develop inconsistencies that may be addressed by the adherence of a patch, such as a doubler, to the portion of the workpiece that contains the inconsistency. For example, the vehicular structures, such as airframes, ship hulls or the like, may develop inconsistencies that may be remedied by the application of a patch to the portion of the structure exhibiting the inconsistency. Similarly, building structures, such as bridge girders, support columns or the like, may develop inconsistencies to which a patch may be applied.
In order to remedy an inconsistency within a workpiece, a patch may be adhered to the portion of the workpiece that exhibits the inconsistency. The patch may be formed of a metal or composite material depending upon the underlying workpiece. In order to adhere a patch to the portion of the workpiece that exhibits an inconsistency, a paste adhesive may be utilized to form the bonded joint between the patch and the underlying workpiece. A paste adhesive is generally a multi-component resin that is mixed uniformly into a paste for application and, as such, is distinct from a film adhesive. However, the use of paste adhesives in a bondline may introduce voids and/or porosity within the bondline once the patch and the workpiece have been cured and bonded together. Voids and/or porosity may reduce the mechanical properties that are otherwise anticipated to be exhibited by the adhesive. The formation of voids and/or porosity and the resulting reduction in the mechanical properties of the adhesive is particularly problematic with paste adhesives that have high viscosities since paste adhesives having higher viscosities tend to not flow sufficiently, thereby retaining entrapped air in the bondline to a greater degree than paste adhesives that have lower viscosities.
In an effort to reduce the voids and/or porosity, high pressure autoclaves have been utilized. However, high pressure autoclaves may not be feasible to be utilized in many cases depending upon, for example, the size and shape of the workpiece, the location of the workpiece, e.g., in the field, etc.
A workpiece having a patch adhered to it with a bond line that includes voids and/or porosity may be used in its existing condition taking into account the reduction in the mechanical properties of the adhesive. Alternatively, the patch may be reprocessed in an effort to improve the mechanical properties. For example, the patch that was previously adhered to the workpiece may be removed and a different patch may be adhered to the workpiece in an effort to bond the patch to the workpiece with an adhesive and process that creates fewer voids and/or porosity. While such reprocessing may sometimes improve the mechanical properties of the adhesive, such reprocessing is inefficient and may delay the eventual return of the workpiece to service.